Coffee machines are in general use in offices, plants, and homes. The machines in issue are the type which are ready to make coffee immediately by maintaining a reservoir of heated water by thermostatic control with the hot water displaced to the brew pot upon the user pouring cold water into the machine.
During periods of inactivity the average user leaves the machine connected so that a supply of heated water is maintained. Without a water vapor saver, the water evaporates to atmosphere and the operational water level in the tank drops substantially. When a user then activates the machine by pouring a measured volume of cold water into it to make a desired quantity of coffee, the measured volume is depleted by the volume previously evaporated so that the desired quantity is not obtained. This is occasioned by the fact that the water reservoir must first be brought up to operational level from which it has dropped due to evaporation.
This causes dissatisfaction with the machine. The fact that it is the user's carelessness which causes the depletion of water does not excuse what the user regards as a mal-function. The machine thus loses desirability through no fault of its own.